Method and composition for chemically polishing metals



respects.

United States Patent Ofifice 3,072,515 Patented Jan. 8, 1953 3,072,515 METHOD AND COlViPOSlTlN FGR CHEMICAILLY POLISHING METALS Alfred von Smolinski, Chicago, Neil W. Berst, Evanston,

and Leslie L. Alt, Chicago, Ill., assignors to The Diversey Corporation, a corporation of illinois N0 Drawing. Filed Mar. 9, 1959, Ser. No. 797,893

12 Claims. (Cl. 156--20) This invention relates to a method and composition for descaling and chemically polishing metals, and relates particularly to descaling and polishing stainless steel surfaces.

During the fabrication of articles made of stainless steel the articles are often welded, brazed or subjected to some other heat treatment which produces a heat scale. This heat scale is not only unsightly but also may tend to aggravate the corrosion of the article, and consequently it must be removed by either mechanical or chemical means. In addition to requiring the removal of the heat scale, stainless steel is often subjected to polishing operations in order to improve the appearance as well as the corrosion resistance thereof.

Methods for descaling, polishing and brightening stainless steel surfaces include mechanical polishing and buffing, electro-polishing and chemical polishing. Mechanical polishing involves extensive handling of the work, resulting in high labor costs, and often cannot be performed at all because of the intricate form and nature of the work requiring polishing. Electro-polishing often produces satisfactory results but requires the use of expensive equipment and large quantities of electrical energy. Although certain chemical baths for brightening stanless steel are known, some of these baths produce a grainy or satiny surface as contrasted to a polished surface; others are rather sensitive to changes in the concentration of the active ingredients and are, therefore, difiicult to work with. in addition, the concentration of the active ingredients in these brightening baths is generally quite high, resulting in high drag-out losses, i.e., the material which clings to an article on leaving a bath and is lost or transferred as a contaminant to subsequent treating operations. Moreover, the prior chemical baths have a tendency to remove unduly large quantities of metal from the article thus adversely affecting the dimensional accuracy of the article, a matter of great importance in some instances.

, it has been discovered that stainless steel may be easily .descaled and brightened with an aqueous solution of hydrochloric acid, nitric acid, and an additive characterized by having a polyoxyethylene chain in its molecule, as hereinafter more fully described. 'In the absence of the additive the nitric acid-hydrochloric acid mixture produces a non-uniformly etched dull surface. The additive modifies the action of the bath so that the surface is polished to a smooth, near-mirror finish while the dissolution of the base metal is kept at a minimum.

By way of definition of terms used in the description of the invention, it should be understood that the term stainless steel is meant to cover those metals being mainly alloys of iron, chromium, and nickel along with other minor constituents, or of only iron and chromium along with minor constituents.

In the'examples and in the appended claims the concentrations of acids are expressed as percent by weight of the total bath, with the acids being considered of 100% strength.

The process of the invention is advantageous in several In addition to using relatively low-cost ingredients, the working solutions are used at low concentrations, thereby minimizing drag-out losses. In addition, no hydrofluoric acid is used, an ingredient which is commonly used in stainless steel descaling solutions, and which is quite toxic. Moreover, because of the relatively small removal of base metal occasioned by the process of the invention, variations in the size of the finished object are kept to a minimum.

In carrying out the process of the invention, there is used a bath comprising an aqueous solution containing about 1% to 10% by weight of hydrochloric acid, about 1% to 8% by weight of nitric acid and about 0.1% to about 20%, and preferably about 0.2% to 15%, of a compound selected from the group consisting of: (l) condensation products of 1 mole of phenol with about 5-30 moles of ethylene oxide, (2) condensation products of 1 mole of an alkyl phenol having up to about 15, and preferably up to about 12, carbon atoms in the alkyl group with about 5-30 moles of ethylene oxide, (3) condensation products of 1 mole of an alkyl amine having about 10-20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (4) condensation products of 1 mole of an aliphatic alcohol having about 10-20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (5) condensation products of 1 mole of a polypropylene glycol containing about 10-50 propylene oxide units with about 4-150 moles of ethylene oxide, and (6) mixtures thereof. it can be seen that the additives used in the invention are characterized by the presence of at least one polyoxyethylene chain within the molecule, i.e., a chain composed of recurring (-O- CH -CH groups. The number of moles of ethylene oxide, which are condensed with one mole of parent compound (i.e., alkyl phenol, alkyl amine, or aliphatic alcohol), depends on the molecular weight of the hydrophobic portion of the condensation product. The additives of the invention should contain sufficient ethylene oxide units to insure the solubility thereof in the acid bath. In general, compounds which are soluble in the acid bath can be formed by condensing the reactants in the proportions given above.

The alkyl phenols which are condensed with ethylene oxide to give one of the additives of the invention are those in which the alkyl group contains 0 to about 15, and preferably 0 to about 12, carbon atoms in a straight or branched chain, which can be saturated or unsaturated. Particularly preferred additives comprise the condensation products of one mole of isooctylphenol or nonylphenol, condensed with about 10 moles of ethylene oxide. Examples of other suitable alkyl phenolethylene oxide condensation products are those in which the hydrophobic portion of the product is derived from phenol, methylphenol (cresol), ethylphenol, hexylphenol, decylphenol, dodecylphenol and the like.

Among the other ethylene oxide condensation products which are used in the invention are those wherein an alkyl amine or aliphatic arcohol, in which the alkyl group in each case has about 10 to about 20 carbon atoms in a straight or branched chain, which can be saturated or unsaturated, is condensed with about 5 to 50 moles of ethylene oxide. Examples of suitable compounds are the condensation products of ethylene oxide with decylamine, dodecylamine, tridecylamine, hexadecylamine, octadecylamine, and the like; and with decyl alcohol, dodecyl alcohol, tridecyl alcohol, hexadccyl alcohol, octadecyl alcohol and the like.

A further class of ethylene oxide condensation products which can be used in the invention is that in which a polypropylene glycol is used as the parent compound. The polypropylene glycol should be normally water-insoluble, i.e., it should be composed of more than about 10 propylene oxide units, suitably about 10-50 propyiene oxide units. For use in the invention, such a polypropylene glycol is condensed with sufficient ethylene oxide to insure the solubility of the product in the polishing bath,

e.g., about 4 to 160 moles of ethylene oxide per mole of glycol.

It has been determined that for the best descaling and chemical polishing the bath preferably contains about 2% to 8% by weight of hydrochloric acid, about 2% to 6% of nitric acid and about 0.2% to 15% of the additive. A preferred specific embodiment of the polishing bath of the invention comprises 3% by Weight of hydrochloric acid, 3% by weight of nitric acid, 1% by weight of the condensation product of 1 mole of isooctylphenol with about 10 moles of ethylene oxide, and the remainder water. Optionally, there may be included in this preferred embodiment about 20% of phosphoric acid.

It has been found that the action of the polishing bath of the invention is enhanced by the addition thereto of phosphoric acid. Phosphoric acid appears to inhibit pitting and stabilize the polishing bath. The phosphoric acid may be used in a concentration up to 60% by weight of the total bath, and preferably between 15% and 35% by weight.

The metal to be polished is suspended in a hot bath at a temperature of about 130-200 F., and preferably within the range from about 160 to 190 F. The time required to produce a polished surface will vary somewhat depending on the composition and temperature of the bath, the type of metal surface to be polished, and the condition of the surface. For normal polishing in the absence of heat scale the time required is ordinarily about to 15 minutes.

The following examples of the invention are given for illustration only and it is not intended that the claims be limited to the specific concentrations of these examples.

EXAMPLE 1 Panels of 24 gauge stainless steel, Type 302, having a 2B (matte) finish were given a preliminary alkaline cleaning to remove oil, grease and the like and were then immersed in a polishing bath consisting of 3% by weight of hydrochloric acid, 3% of nitric acid, 1% of the condensation product of 1 mole of isooctylphenol with moles of ethylene oxide, 24% of phosphoric acid. and the remainder water, the bath being maintained at a temperature of 190 F. After 5 minutes of immersion the panels were withdrawn, soaked in water for 2 minutes and then returned to the bath for a further 2 minutes at the end of which time they were removed, washed, rinsed and inspected. As a result of this treatment the panels acquired a bright, smooth, near-mirror finish.

EXAMPLE 2 Example 1 was repeated using a bath (3% hydrochloric acid, 3% nitric acid) containing no additive. No brightening or polishing of the panels resulted from the treatment. In addition, non-uniform etching of the panels was observed.

EXAMPLE 3 Example 1 was repeated using a bath containing 5% hydrochloric acid, 3% nitric acid, and 1% of the same additive. Results equivalent to those of Example 1 were obtained.

EXAMPLE 4 Example 1 was repeated using 3% hydrochloric acid, 5% nitric acid, and 1% of the same additive in the bath. Equivalent results were obtained.

EXAMPLE 5 Example 1 was repeated using 3% hydrochloric acid, 3% nitric acid, phosphoric acid and 1% additive (isooctylphenol-ethylene oxide condensation product) in the bath which was maintained at 160 F. Equivalent results were obtained after a total immersion time of about minutes.

EXAMPLES 6, 7, AND 8 Example 1 was repeated using a bath comprising 3% hydrochloric acid, 3% nitric acid, 24% phosphoric acid 4 and 1% of the additives identified below. Brightening and polishing of the steel panels were obtained in each case.

Pipe couplings of forged stainless steel (Types 304 and 316) having a black surface coting of heat scale from prior heat treatment were subjected to the polishing action of the bath of Example 1. After a total immersion of about 10 to 20 minutes, at a temperature of F., the pipe couplings became bright and free of scale.

EXAMPLE 10 There was prepared an article consisting of a piece of stainless steel having attached thereto by means of silver solder pieces of mild steel, copper and brass. The soldering had caused the formation of a heavy, blue-black heat scale on the stainless steel. This article was treated with the bath of Example 1 at 190 F. for a total of 10 minutes. As a result of this treatment, the stainless steel was clean and bright, the copper and brass were clean, the mild steel had evidence of a light attack, and there was practically no attack on the silver solder. There was furthermore no evidence of any adverse galvanic action which might have been expected from the presence of the dissimilar metals in contact with an electrolyte.

The baths of the invention are useful in the descaling and polishing of stainless steels generally. Particularly good results, however, have been obtained in polishing the 300 Series of stainless steels which contain about 18% chromium in addition to about 8% of nickel. Surfaces which are somewhat less bright though still clean are obtained with the 200 Series (low nickel) of stainless steels and with the 400 Series which contain no nickel. In addition, the polishing baths of the invention can be used to advantage in treating special steels and other special alloys.

For handling and storage purposes the polishing bath of the invention may be supplied in a concentrated mixture to which is added nitric acid and water to make the working solution. Concentrates of this type may suitably contain about 6% to 9% by weight of hydro chloric acid, about 2% to 3% of the additive, optionally about 25% to 65% of phosphoric acid, and the remainder Water. A particularly preferred example of such a concentrate. contains about 8% by weight of hydrochloric acid, about 60% of phosphoric acid, about 2.6% of the condensation product of 1 mole of isooctylphenol with about 10 moles of ethylene oxide, and the remainder water.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

1. A bath for chemically polishing and descaling stainless steel surfaces which consists essentially of an aqueous solution containing about 2% to 10% by weight of hydrochloric acid, about 1% to 8% of nitric acid, about 0.1% to 20% of a compound selected from the group consisting of: 1) condensation products of 1 mole of phenol with about 530 moles of ethylene oxide, (2) condensation products of 1 mole of an alkyl phenol having up to about 15 carbon atoms in the alkyl group with about 5-30 moles of ethylene oxide, (3) condensation products of 1 mole of an alkyl amine having about -20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (4) condensation products of 1 mole of an aliphatic alcohol having about 10-20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (5) condensation products of 1 mole of a polypropylene glycol containing about 10-50 propylene oxide units with about 4-160 moles of ethylene oxide, and (6) mixtures thereof, and the remainder water.

2. The bath of claim 1 in which said compound is the condensation product of 1 mole of isooctylphenol with about 10 moles of ethylene oxide.

3. The bath of claim 1 wherein said compound is the condensation product of 1 mole of nonylphenol with about 10 moles of ethylene oxide.

4. The bath of claim 1 which includes about -35% of phosphoric acid.

5. The bath of claim 1 which contains said compound in an amount of about 0.2% to 15% by weight.

6. A bath for chemically polishing and descaling stainless steel surfaces which consists essentially of about 3% by weight of hydrochloric acid, about 3% of nitric acid, about 1% of the condensation product of 1 mole of isoactylphenol with about 10 moles of ethylene oxide, and the remainder water.

7. The bath of claim 6 which includes about of phosphoric acid.

8. The method of descaling and polishing a stainless steel surface which comprises contacting said surface with an aqueous solution consisting essentially of about 2% to 10% by weight of hydrochloric acid, about 1% to 8% of nitric acid, about 0.1% to 20% of a compound selected from the group consisting of: (1) condensation products of 1 mole of phenol with about 5-30 moles of ethylene oxide, (2) condensation products of 1 mole of an alkyl phenol having up to about 15 carbon atoms in the alkyl group with about 5-30 moles of ethylene oxide, (3) condensation products of 1 mole of an alkyl amine having about 10-20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (4) condensation products of 1 mole of an aliphatic alcohol having about 10-20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (5) condensation products of 1 mole of a polypropylene glycol containing about 10-50 propylene oxide units with about 4-150 moles of ethylene oxide, and (6) mixtures thereof, and the remainder water for a period of time and at an elevated temperature sufiicient to remove scale and produce a bright polished surface.

9. The method of claim 8 wherein said solution includes about 15-35% of phosphoric acid.

10. The method of claim 8 wherein said temperature is within the range from about F. to about F.

11. A concentrated mixture for preparing a bath for chemically polishing and descaling stainless steel which consists essentially of about 6% to 9% by weight of hydrochloric acid, about 25% to 65% of phosphoric acid, about 2% to 3% of the condensation product of 1 mole of isooctylphenol with about 10 moles of ethylene oxide,

and the remainder Water.

12. A concentrated mixture for preparing a bath for chemically polishing and descaling stainless steel which consists essentially of about 8% by weight of hydrochloric acid, about 60% of phosphoric acid, about 2.6% of the condensation product of 1 mole of isooctylphenol with about 10 moles of ethylene oxide, and the remainder water.

References Cited in the file of this patent UNITED STATES PATENTS 2,393,868 Wassell Jan. 29, 1946 2,446,060 Pray et al. July 27, 1948 2,461,228 Miles Feb. 8, 1949 2,585,127 Holman et al. Feb. 12, 1952 2,628,199 Lowenheim Feb. 10, 1953 2,630,457 Hansen Mar. 3, 1953 2,672,449 Snell Mar. 16, 1954 2,694,001 Hayes et al. Nov. 9, 1954 2,849,297 Wisken Aug. 26, 1958 2,854,444 Monson et a1. Sept. 30, 1958 2,856,434 Niederhauser et al. Oct. 14, 1958 2,890,944 Hays June 16, 1959 2,940,837 Asker June 14, 1960 2,942,956 Kelly June 28, 1960 

1. A BATH FOR CHEMICALLY POLISHING AND DESCALING STAINLESS STEEL SURFACES WHICH CONSISTS ESSENTIALLY OF AN AQUEOUS SOLUTION CONTANING ABOUT 2% TO 10% BY WEIGHT OF HYDROCHLORIC ACID, ABOUT 1% TO 8% OF NITRIC ACID, ABOUT 0.1% TO 20% OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF: (1) CONDENSATION PRODUUCTS OF 1 MOLE OF PHENOL WITH ABOUT 5-30 MOLES OF ETHYLENE OXIDE, (2) CONDENSATION PRODUCTS OF 1 MOLES OF AN ALKYL PHENOL HAVING UP TO ABOUT 15 CARBON ATOMS IN THE ALKYL GROUP WITH ABOUT 5-30 MOLES OF ETHYLENE OXIDE, (3) CONDENSATION PRODUCTS OF 1 MOLE OF AN ALKYL AMINE HAVING ABOUT 10-20 CARBON ATOMS IN THE ALKYL GROUP WITH ABOUT 5-50 MOLES OF ETHYLENE OXIDE, (4) CONDENSATION PRODUCTS OF 1 MOLE OF AN ALIPHATIC ALCOHOL HAVING ABOUT 10-20 CARBON ATOMS IN THE ALKYL GROUP WITH ABOUT 5-50 MOLES OF ETHYLENE OXIDE, (5) CONDENSATION PRODUCTS OF 1 MOLE OF A POLYPROPYLENE GLYCOL CONTAINING ABOUT 10-50 PROPYLENE OXIDE UNITS WITH ABOUT 4-160 MOLES OF ETHYLENE OXIDE, AND (6) MIXTURES THEREOF, AND THE REMAINDER WATER.
 8. THE METHOD OF DESCALING AND POLISHING A STAINLESS STEEL SURFACE WHICH COMPRSES CONTACTING SAID SURFACE WITH AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF ABOUT 2% TO 10% BY WEIGHT OF HYDROCHHLORIC ACID, ABOUT 1% TO 8% OF NITIRC ACID, ABOUT 0.1% TO 20% OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF: (1) CONDENSATION AN ALKYL PHENOL HAVING UP TO ABOUT 15 CARBOB ATOMS IN PRODUCTS OF 1 MOLE OF PHENOL WITH ABOUT 5-30 MOLES OF ETHYLENE OXIDE, (2) CONDENSATION PRODUCTS OF 1 MOLE OF THE ALKYL GROUP WITH BOUT 5-30 MOLES OF ETHYLENE OXIDE, (3) CONDENSATION PRODUCTS OF 1 MOLE OF AN ALKYL AMINE HAVING ABOUT 10-20 CARBON ATOMS IN THE ALKYL GROUP WITH ABOUT 5-50 MOLES OF ETHYLENE OXIDE, (4) CON: DENSATION PRODUCTS OF 1 MOLE OF AN SLIPHATIC ALCOHOL HAVING ABOUT 10-20 CARBON ATOMS IN THE ALKYL GROUP WITH ABOUT 5-50 MOLES OF ETHYLENE OXIDE, (5) CONDENSATION PRODUCTS OF 1 MOLE OF A POLYPROPYLENE GLYCOL CONTAINING ABOUT 10-50 PROPYLENE OXIDE UNITS WITH ABOUT 4-150 MOLES OF ETHYLENE OXIDE, AND (6) MIXTURES THEREOF, AND THE REMAINDER WATER FOR A PERIOD OF TIME AND AT AN ELEVATED TEMPERATURE SUFFICIENT TO REMOVE SCALE AND PRODUCE A BRIGHT POLISHED SURFACE. 